1. Field of the Invention
The present invention relates to a semiconductor device including both digital and analog circuits, and electronic equipment using such a semiconductor device. The present invention further relates to electronic equipment in which an amplification factor in the amplifier is variable, and to a semiconductor device to be used in such electronic equipment.
2. Description of the Related Art
There is a case that some semiconductor devices require both digital and analog circuits mounted thereon. Analog circuits include those driven at a DC voltage and those driven using sine curve oscillation signals with a specified frequency. On the other hand, digital circuits are driven at a drive frequency of several megahertz (MHz) because of high-speed operation. Thus, digital circuits are driven at a drive frequency significantly higher than analog circuits.
In such a semiconductor device, a digital circuit driven at a high drive frequency becomes a source of noise which adversely affects an analog circuit driven at a lower frequency.
In some analog circuits, signals input into a semiconductor device are amplified by an amplifier and passed through a filter, then the input signal levels are detected by comparing them with a reference potential using a comparator.
This type of semiconductor device has a problem in that the detection level cannot be easily varied by the users, requiring design modification of the semiconductor device.
An object of the present invention is, therefore, to provide a semiconductor device which can reduce an adverse effect of noise caused by digital circuits driven at a comparatively high frequency on analog circuits which are driven at a lower frequency, and can achieve reduction in size of digital circuits, and to provide electronic equipment using such a semiconductor device.
Another object of the present invention is to provide electronic equipment which has a function of detecting the levels of input signals using an amplifier and a comparator, and can easily modify the detection level without changing the reference potential in the comparator, and to provide a semiconductor device used in such electronic equipment.
In one aspect of the present invention, a semiconductor device comprises: a power supply circuit; and a plurality of functional blocks to each of which a voltage is supplied from the power supply circuit, wherein the power supply circuit has a voltage generation circuit for generating a second voltage by reducing a first voltage which is supplied from an external power supply source; and wherein at least one of the plurality of functional blocks comprises: an analog circuit to which the first voltage is supplied and which is driven at a first drive frequency; a digital circuit to which the second voltage is supplied and which is driven at a second drive frequency being higher than the first drive frequency; and a level shifter which is disposed between the analog circuit and the digital circuit and shifts a signal level which is input or output between the analog circuit and the digital circuit.
In this aspect of the present invention, a lower voltage than that supplied to the analog circuit is supplied to the digital circuit which is driven at a drive frequency higher than that of the analog circuit. Therefore, noise from the digital circuit which is a source of the noise is weakened and the adverse effect on the analog circuit is reduced.
When a signal is input or output between the analog circuit and the digital circuit which are driven at different voltages, signal levels can be shifted by the level shifter so that the signal levels conform to the drive voltage.
An input terminal of a grounding voltage supplied to the analog circuit may differ from an input terminal of a grounding voltage supplied to the digital circuit.
The use of different input terminals can reduce the adverse effect of noise on the analog circuit compared to the use of a common input terminal.
In the above-described aspect, the voltage resistance of transistors in the digital circuit can be lower than that in the analog circuit. Therefore, a channel length of a semiconductor transistor forming the digital circuit may be shorter than a channel length of a semiconductor transistor forming the analog circuit. This ensures reduction in the size of the digital circuit. In addition, a gate oxide film of a semiconductor transistor forming the digital circuit may be thinner than a gate oxide film of a semiconductor transistor forming the analog circuit.
The analog circuit and the digital circuit may respectively have two wiring layers consisting of an upper wiring layer and a lower wiring layer. The analog circuit and the digital circuit may respectively have a crossing section of the two wiring layers, the upper wiring layer of the analog circuit being disposed without crossing the upper wiring layer and the lower wiring layer of the digital circuit, and the lower wiring layer of the analog circuit being disposed without crossing the upper wiring layer and the lower wiring layer of the digital circuit. The adverse effect of noise can be reduced in this manner.
In another aspect of the present invention, a semiconductor device comprises: a power supply circuit; and a functional block to which a voltage is supplied from the power supply circuit, wherein the power supply circuit has a voltage generation circuit for generating a second voltage VD1 by reducing a first voltage VDD which is supplied from an external power supply source; and wherein the functional block comprises: a first analog circuit to which the first voltage VDD is supplied from a first terminal and which is driven at a DC voltage; a second analog circuit to which a voltage AVDD having the same potential as the first voltage VDD is supplied from a second terminal and which is driven at a first drive frequency; a digital circuit to which the second voltage VD1 is supplied from the voltage generation circuit and which is driven at a second drive frequency being higher than the first drive frequency; and a level shifter which is disposed among the first and the second analog circuits and the digital circuit for shifting signal levels which are input or output among the first and the second analog circuit and the digital circuit.
In this aspect of the present invention, a voltage lower than that supplied to the first and second analog circuits is supplied to the digital circuit which is driven at a drive frequency higher than the second analog circuit. Therefore, noise from the digital circuit which is a source of noise is weakened and the adverse effect of noise on the second analog circuit is reduced.
When a signal is input or output among the first and the second analog circuits and the digital circuit which are respectively driven at different voltages, signal levels can be shifted by the level shifter so that the signal levels conform to the drive voltage.
The semiconductor device according to this aspect further comprises a first terminal for inputting the voltage VDD into the first analog circuit and a second terminal for inputting the voltage AVDD to the second analog circuit. This makes it possible to use wiring for supplying the voltage AVDD different from the wiring for supplying the voltage VDD, and to make the former wire shorter than the latter wire. Providing separate wiring reduces the adverse effect of voltage fluctuation caused by the digital circuit side connected with the voltage VDD on the second analog circuit. In addition, because the impedance can be reduced by reducing the length of the wiring for supplying the voltage AVDD, it is possible to decrease the power supply voltage fluctuation (impedancexc3x97current) when a current flows through the wiring in the second analog circuit.
In this aspect of the present invention, an input terminal of the ground voltage VSS supplied to the first analog circuit and the digital circuit may differ from an input terminal of the ground voltage AVSS supplied to the second analog circuit. This makes it possible to use separate supply lines to grounding voltages and, at the same time, to reduce the impedance of the wiring for supplying the voltage AVSS. Consequently, an adverse effect of the digital circuit and a supply voltage fluctuation in the second analog circuit are decreased.
The use of the above-described semiconductor device in electronic equipment not only reduces occurrence of malfunctioning of the electronic equipment as an adverse effect due to noise can be reduced, but also ensures reduction in size of the electronic equipment because the semiconductor device can be densely integrated by miniaturizing digital circuits.
In further aspect of the present invention, electronic equipment comprises a semiconductor device which includes an amplification circuit and a comparing circuit which compares an output from the amplification circuit and a reference value to detect a signal of a specified level, wherein the amplification circuit has an input resistor and a feed back resistor connected thereto, and at least one of the input resistor and the feed back resistor is externally installed resister provided outside the semiconductor device.
This constitution allows the amplification factor of input signals to be varied by arbitrarily setting the amplification factor using the external resistor, while maintaining the reference voltage in the comparing circuit at a specified value. This consequently allows arbitrary change of the detection level in the comparator.
In this instance, the semiconductor device mounted on the electronic equipment may be capable of selecting one of two conditions in which: the semiconductor device incorporates the input resistor and the feed back resistor which are connected to the amplification circuits in one condition; and at least one of the input resistor and the feed back resistor is externally installed in the semiconductor device by a mask option in the other condition.